Subject: [PATCH 19/22] KVM: arm/arm64: vgic: Don't rely on the wrong pending table

From: Marc Zyngier <[email-masked]>
Date: Wed, 20 Nov 2019 16:42:33 +0000

From: Zenghui Yu <[email-masked]>

It's possible that two LPIs locate in the same "byte_offset" but target
two different vcpus, where their pending status are indicated by two
different pending tables.  In such a scenario, using last_byte_offset
optimization will lead KVM relying on the wrong pending table entry.
Let us use last_ptr instead, which can be treated as a byte index into
a pending table and also, can be vcpu specific.

Fixes: 280771252c1b ("KVM: arm64: vgic-v3: KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES")
Cc: [email-masked]
Signed-off-by: Zenghui Yu <[email-masked]>
Signed-off-by: Marc Zyngier <[email-masked]>
Acked-by: Eric Auger <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
---
 virt/kvm/arm/vgic/vgic-v3.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index e69c538a24ca..f45635a6f0ec 100644
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -363,8 +363,8 @@ int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq)
 int vgic_v3_save_pending_tables(struct kvm *kvm)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
-	int last_byte_offset = -1;
 	struct vgic_irq *irq;
+	gpa_t last_ptr = ~(gpa_t)0;
 	int ret;
 	u8 val;
 
@@ -384,11 +384,11 @@ int vgic_v3_save_pending_tables(struct kvm *kvm)
 		bit_nr = irq->intid % BITS_PER_BYTE;
 		ptr = pendbase + byte_offset;
 
-		if (byte_offset != last_byte_offset) {
+		if (ptr != last_ptr) {
 			ret = kvm_read_guest_lock(kvm, ptr, &val, 1);
 			if (ret)
 				return ret;
-			last_byte_offset = byte_offset;
+			last_ptr = ptr;
 		}
 
 		stored = val & (1U << bit_nr);
-- 
2.20.1

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